This invention relates to generator and turbine machinery. More particularly, it relates to a laser based ablation method for cleaning generator and turbine components.
Laser machining processes transport photon energy into target material in the form of thermal energy or photochemical energy, they remove material by melting and blow away, or by direct vaporization/ablation processes. On the other hand, traditional machining processes rely on mechanical stresses induced by tools to break molecular bonds created in the target material.
Traditional solutions for removing contaminated or unwanted surface coatings involved grinding the surface with abrasives or chemically treating the surface with solvents or acids to lift the surface coating for scraping. EPA and OSHA restrictions on solvents and acids have forced modern industry to turn increasingly to two alternatives: (1) sandblasting, or other pneumatically driven particulate, and (2) water jetting. When cleaning an exposed area with these typical materials, they also become contaminated as they come into contact with the contaminated surface. Thus, these conventional cleanup efforts add volume to the waste stream and, in hazardous situations, require additional treatment of the material used in the cleaning or cutting process.
Usually, the first step in the surface preparation process is to mechanically remove rust or debris from the substrate. Wiping loose dust and dirt of f the part is an example of mechanical cleaning. Typically, though, more aggressive mechanical action is needed to remove rust or other contaminates. Rust and metal scales can be removed mechanically by sanding, brushing with a wire brush or plastic xe2x80x9cwoolxe2x80x9d pads, or by using abrasive blasting techniques. Abrasive blasting can also be used for removing old paint from products, and solvent-based chemical stripping is another option.
For generator or turbine components, after a generator rotor is removed from the stator, internal components need to be cleaned for maintenance, any needed repairs or a partial or full rewind of a system. Cleaning involves removing dust, oily deposits and other surface contamination. For example, if the old rotor windings are removed for a rewind, then cleaning involves removal of residual insulation and resins from the coil slots in rotor forging. Likewise, if the rotor coils are to be reused, removal of insulation and resins from the coils is also required. Exemplary components requiring cleaning include generator stator core, stator end windings, rotor forging, retaining rings, to name but a few.
The current methods of cleaning generator stator core are essentially manual, using scrapers made of textolite, wiping with rags soaked in approved cleaning solutions, and final cleaning with clean dry rags. Corncob blasting has also been used on stator end windings that have been heavily contaminated as a result of winding failure. Rotor forging and rotor coils to be reused are cleaned by blasting with glass beads. Rotor coils wrapped with glass mica tape are heated in an oven to burn off the tape and subsequently cleaned with approved solvents and rags.
Laser ablation can clean the components with no damage to the parent material and at the same time significantly reduce the amount of waste products generated. Laser ablation efficiently removes selected surface contaminants from generator components without damaging the parent materials and thus significantly reduces the waste products generated.
As described above, several different methods are being used to clean components of generator stator and rotor. Containing, removing and disposing of the used glass beads and corn cob processes related to collecting and disposing of the contaminated rags after cleaning pose an environmental hazard. Workmen are exposed to hazardous chemical cleaners and are subjected to potential exposure to airborne contamination of the media used for blast cleaning. The blast cleaning media can escape from the enclosure and contaminate the surrounding area. Thus, there is a need to overcome the problems faced by prior approaches.
These methods of cleaning are very labor intensive and generates considerable amount of waste material that has to be disposed of. Some of the cleaning solvents used are classified as hazardous. Thus, there is a need to overcome the above-identified problems faced by traditional techniques.
Accordingly, the present invention provides a laser ablation method and apparatus to clean generator and turbine components overcoming problems faced by prior methods. The laser ablation method of the present invention uses short pulses of a laser to cause very localized deposits of energy causing surface deposits to vaporize and explode, and thereby releasing the contaminant deposits from the surface they are attached to. Contaminant vapors are then removed and filtered by a vacuum collection system. The laser ablation method of the present invention significantly reduces waste products due to the vaporization of contaminants during removal.
Specifically, the apparatus of the present invention includes a laser source, a modulator for modulating a laser beam generated by the laser source to ablate a contaminated surface of a machine component. During operation, a laser beam is directed at a surface of a machine component to be cleaned. On the surface, the contaminated material to be removed is heated rapidly to vaporize the material while ensuring that the material properties of the parent material/base material of the machine component remain unchanged. Preferably, the surface temperature of the base material of the machine component that is being cleaned is not changed, thereby preventing any mechanical or thermal damage or change in material properties of the base material.
In one aspect, the present invention relates to a method of cleaning a generator or turbine component using a laser, the method comprising programming a controller coupled to a laser source for controlling the laser source to perform laser ablation; directing a laser beam at a generator or turbine component surface for vaporizing surface contaminants and coatings deposited on said generator or turbine component surface without changing base material properties of said generator or turbine components. The method further includes coupling the controller to a computer system having a processor and a database; loading the database with turbine or generator component data and corresponding laser power related data for ablating surface contaminants and coatings from the turbine or generator components; providing a detector to monitor ablation process and provide feedback data to the computer system; comparing the feedback data with predetermined data to determine progress of ablation; and controlling the laser source depending on the comparison step, and disposing vapors generated during laser ablation.
In another aspect, a laser based system for removing contaminants deposited on a machine component surface, comprises a laser source; a controller for controlling the laser source, the controller causing the laser to emit a laser beam such that the contaminants deposited on the machine component surface are ablated without changing base material properties of the machine component. The controller is preferably programmed to control the laser source. The system further includes a computer system coupled to the controller; a detector disposed adjacent the generator or turbine component to monitor the progress of laser ablation using the laser beam from the laser source, the detector providing the monitored data to the computer system for causing the controller to vary the power of the laser beam from the laser source. The computer system preferably includes a processor having a comparator; and a database for storing turbine or generator component data, and respective laser power related data for causing laser ablation of surface contaminants and coatings of the turbine or generator components.
In another aspect, a laser-based system for cleaning a generator or turbine component, comprises a controller coupled to a laser source for controlling the laser source to perform laser ablation; means for directing a laser beam at a generator or turbine component surface for vaporizing surface contaminants and coatings deposited on the generator or turbine component surface without changing base material properties of the generator or turbine component. The system also includes a computer system having a processor and a database, the computer system communicatively coupled to the controller, and wherein the database is loaded with turbine or generator component data and corresponding laser power related data for ablating surface contaminants and coatings from the turbine or generator components; a detector disposed adjacent to the turbine or generator component to monitor ablation process and provide feedback data to the computer system; a comparator for comparing the feedback data with predetermined data to determine progress of ablation; and means for controlling the laser source depending on the comparison step.
In a further aspect, the present invention provides a laser-based method for cleaning a machine component, the method comprising controlling a laser source to modulate a laser beam for performing laser ablation; directing the laser beam towards a component surface for vaporizing surface contaminants and coatings deposited on the component surface without changing base material properties of the component; communicatively coupling a computer system having a processor and a database to the controller; loading the database with data related to the component and corresponding laser power related data for ablating contaminants and coatings from the turbine or generator components; monitoring ablation process of the component using a detector, the detector being disposed adjacent to the component; receiving feedback data from the detector at the computer system; comparing the feedback data with predetermined data in a comparator to determine progress of ablation; and controlling the laser source depending on the comparison step.
In yet another aspect, the present invention provides an apparatus for cleaning a generator or turbine components using a laser beam, the apparatus including means for controlling a laser source to perform laser ablation; and means for directing a laser beam at a generator or turbine component surface for vaporizing surface contaminants and coatings deposited on the generator or turbine component surface without changing base material properties of the generator or turbine components.